Epoxide and thioepoxide functional, polymerizable compositions and methods of preparing optical articles therefrom

ABSTRACT

Provided is a thioepoxide functional polymerizable composition comprising a reaction product of thiourea and an epoxide functional, polymerizable composition. The epoxide functional, polymerizable composition comprises a reaction product prepared from a reaction mixture comprising:
         (a) a monomer comprising at least one ethylenically unsaturated ester functional monomer having an epoxide functional group; and   (b) a compound having two or more thiol groups.       

     The reactants (a) and (b) are reacted via a Michael addition reaction in the presence of a base to form an epoxide functional reaction product. Also provided are methods of preparing an optical article using the polymerizable compositions.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.13/706,178, filed on Dec. 12, 2012, incorporated herein by reference inits entirety.

FIELD OF THE INVENTION

The present invention relates to epoxide functional polymerizablecompositions and thioepoxide functional polymerizable compositions thatare derived from ethylenically unsaturated monomers having episulfidefunctional groups in the monomer, and to methods of preparing opticalarticles from such polymerizable compositions.

BACKGROUND OF THE INVENTION

Polymeric materials, such as plastics, have been developed asalternatives and replacements for silica based inorganic glass inapplications such as, optical lenses, fiber optics, windows andautomotive, nautical and aviation transparencies. These polymericmaterials can provide advantages relative to glass, including, shatterresistance, lighter weight for a given application, ease of molding andease of dyeing. Representative examples of such polymeric materialsinclude, poly(methyl methacrylate), polycarbonate and poly(diethyleneglycol bis(allylcarbonate)).

The refractive indices of many polymeric materials are generally lowerthan that of high index glass. For example, the refractive index ofpoly(diethylene glycol bis(allylcarbonate)) is about 1.50, compared tothat of high index glass, which can range, for example, from 1.60 to1.80.

Polymeric materials (polymerizates) prepared from the polymerization ofmonomers containing aromatic rings and/or sulfur typically have highrefractive indices. Polymeric materials having a combination of highrefractive indices, such as at least 1.57, and low levels of chromaticdispersion (e.g., having ABBE numbers of at least 30), can be preparedfrom monomers containing certain heteroatoms, such as sulfur atoms. Suchpolymerizates are very useful in the making of optical elementsrequiring superior optical properties.

It would be desirable to develop polymerizable compositions that providedesirable optical properties to an optical article prepared therefrom,such as high refractive index and high ABBE number, with low cost andsimple processing.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided athioepoxide functional, polymerizable composition comprising a reactionproduct of thiourea and an epoxide functional polymerizable composition.The epoxide functional polymerizable composition comprises a reactionproduct of:

-   -   (a) a monomer comprising at least one ethylenically unsaturated        ester functional monomer having an epoxide functional group; and    -   (b) a compound having two or more thiol groups.        The reactants (a) and (b) are reacted via a Michael addition        reaction in the presence of a base to form an epoxide functional        reaction product.

Also provided are methods of preparing an optical article. In a firstembodiment, the method comprises:

(1) reacting together:

-   -   (a) a monomer comprising at least one ethylenically unsaturated        ester functional monomer having an epoxide functional group; and    -   (b) a compound having two or more thiol groups;        wherein the reactants (a) and (b) are reacted via a Michael        addition reaction in the presence of a base to form an epoxide        functional reaction product;

(2) reacting the epoxide functional reaction product formed in step (1)with thiourea to form a thioepoxide functional, polymerizablecomposition;

(3) mixing the thioepoxide functional, polymerizable composition formedin step (2) with:

-   -   (a) a polymerizable composition comprising at least one        ethylenically unsaturated (meth)acrylate functional monomer        having a thioepoxide functional group;    -   (b) an addition polymerization initiator; and    -   (c) a catalyst to form a reaction mixture;

(4) introducing the reaction mixture formed in step (3) to a mold of adesired shape at a temperature and for a time sufficient to form apolymerizate;

(5) releasing the polymerizate from the mold to yield an opticalarticle.

In a separate embodiment, the method comprises:

-   -   (1) reacting together the following reactants:        -   (a) a monomer comprising at least one ethylenically            unsaturated ester functional monomer having an epoxide            functional group; and        -   (b) a compound having two or more thiol groups;            wherein the reactant (a) is present in stoichiometric excess            and the reactants (a) and (b) are reacted via a Michael            addition reaction in the presence of a base to form a            product mixture comprising an epoxide functional reaction            product and excess monomer (a);    -   (2) reacting the product mixture formed in step (1) with        thiourea to form a thioepoxide functional, polymerizable        composition;    -   (3) preparing a prepolymer reactant mixture by:    -   (i) mixing the thioepoxide functional, polymerizable composition        formed in step (2) with:        -   (a) a first polymerizable composition comprising at least            one ethylenically unsaturated monomer; and        -   (b) an azo addition polymerization initiator to form a            reaction mixture; and    -   (ii) allowing ethylenically unsaturated groups in the reaction        mixture formed in (i) to polymerize to form a prepolymer having        a threshold viscosity of 50 to 500 centipoise measured at 25° C.        wherein the azo addition polymerization initiator is present in        an amount sufficient only to achieve the threshold viscosity;    -   (4) mixing the prepolymer reactant mixture formed in step (3)        with:        -   (a) an initiator package that is essentially free of azo            initiators; and        -   (b) a second polymerizable composition comprising at least            one ethylenically unsaturated monomer having two or more            ethylenically unsaturated groups to form a moldable            composition;    -   (5) introducing the moldable composition formed in step (4) to a        mold of a desired shape at a temperature and for a time        sufficient to form a polymerizate;        -   (6) releasing the polymerizate from the mold to yield an            optical article.

DETAILED DESCRIPTION OF THE INVENTION

As used herein, molecular weight values of polymers, such as weightaverage molecular weights (Mw) and number average molecular weights(Mn), are determined by gel permeation chromatography using appropriatestandards, such as polystyrene standards.

As used herein, polydispersity index (PDI) values represent a ratio ofthe weight average molecular weight (Mw) to the number average molecularweight (Mn) of the polymer (i.e., Mw/Mn).

As used herein, the term “polymer” means homopolymers (e.g., preparedfrom a single monomer species), and copolymers (e.g., prepared from atleast two monomer species).

As used herein, the term “(meth)acrylate” and similar terms, such as(meth)acryloyl and (meth)acrylic acid ester, means methacrylate andacrylate. Either or both, when they exist, may be present in acomposition.

As used herein, the term “thio(meth)acrylate” and similar terms, such asthio(meth)acryloyl and thio(meth)acrylic acid ester, meansthiomethacrylate and thioacrylate, as above.

As used herein, recitations of “linear or branched” groups, such aslinear or branched alkyl, are understood to include: a methylene groupor a methyl group; groups that are linear, such as linear C₂-C₂₅ alkylgroups; and groups that are appropriately branched, such as branchedC₃-C₂₅ alkyl groups.

As used herein, the term “halo” and similar terms, such as halo group,halogen, halogen group, halide, and halide group means F, Cl, Br and/orI, such as fluoro, chloro, bromo and/or iodo.

Unless otherwise indicated, all ranges or ratios disclosed herein are tobe understood to encompass any and all subranges or subratios subsumedtherein. For example, a stated range or ratio of “1 to 10” should beconsidered to include any and all subranges between (and inclusive of)the minimum value of 1 and the maximum value of 10; that is, allsubranges or subratios beginning with a minimum value of 1 or more andending with a maximum value of 10 or less, such as but not limited to, 1to 6.1, 3.5 to 7.8, and 5.5 to 10.

As used herein, the articles “a,” “an,” and “the” include pluralreferents unless otherwise expressly and unequivocally limited to onereferent.

Other than in the operating examples, or where otherwise indicated, allnumbers expressing quantities of ingredients, reaction conditions, andso forth used in the specification and claims are to be understood asmodified in all instances by the term “about.”

The epoxide functional polymerizable compositions of the presentinvention comprise a reaction product prepared from a reaction mixturecomprising: (a) a monomer comprising at least one ethylenicallyunsaturated, ester functional monomer having an epoxide functionalgroup; and (b) a compound having two or more thiol groups (polythiol).Examples of suitable monomers (a) include, for example, glycidyl(meth)acrylate, glycidyl maleates and/or fumarates, and the like. Thepresence of the ester functional group in the epoxide functional monomerallows for Michael addition of the thiol to the ethylenic double bond totake place between the epoxide functional monomer and the polythiol,provided the carbon-oxygen double bond in the ester group is conjugatedwith the ethylenic unsaturation in the monomer.

Suitable polythiols are thiol-containing materials that may have atleast two thiol functional groups and may comprise a dithiol, or amixture of a dithiol and a compound having more than two thiolfunctional groups (higher polythiol). Such mixtures may include mixturesof dithiols, mixtures of higher polythiols and/or mixtures of dithiolswith higher polythiols. The thiol functional groups are typicallyterminal groups, though a minor portion (i.e., less than 50 percent ofall groups) may be pendant along a chain. The compound (b) mayadditionally contain a minor portion of other active hydrogenfunctionality (i.e., different from thiol), for example, hydroxylfunctionality. Thiol-containing materials may be linear or branched, andmay contain cyclic, alkyl, aryl, aralkyl, or alkaryl groups.

Suitable dithiols can include linear or branched aliphatic,cycloaliphatic, aromatic, heterocyclic, polymeric, oligomeric dithiolsand mixtures thereof. The dithiol can comprise a variety of linkagesincluding but not limited to ether linkages (—O—), sulfide linkages(—S—), polysulfide linkages (-Sx-, wherein x is at least 2, or from 2 to4), ester linkages, urethane linkages, and combinations of suchlinkages.

Non-limiting examples of suitable dithiols for use in the presentinvention can include but are not limited to2,5-dimercaptomethyl-1,4-dithiane, bis(2-mercaptoethyl)sulfide(dimercaptodiethylsulfide or “DMDS”), ethanedithiol,3,6-dioxa-1,8-octanedithiol, ethylene glycol di(2-mercaptoacetate),ethylene glycol di(3-mercaptopropionate), poly(ethylene glycol)di(2-mercaptoacetate) and poly(ethylene glycol)di(3-mercaptopropionate), benzenedithiol,4-tert-butyl-1,2-benzenedithiol, 4,4′-thiodibenzenethiol,pentaerythritol tetrakis(2-mercaptoacetate), pentaerythritoltetrakis(3-mercaptopropionate), trimethylolpropanetris(2-mercaptoacetate), trimethylolpropane tris(3-mercaptopropionate),and mixtures thereof.

The dithiol may include dithiol oligomers having disulfide linkages suchas materials represented by the following formula:

wherein n can represent an integer from 1 to 21.

Dithiol oligomers represented by Formula I can be prepared, for example,by the reaction of 2,5-dimeracaptomethyl-1,4-dithiane with sulfur in thepresence of basic catalyst, as known in the art.

The nature of the SH group in polythiols is such that oxidative couplingcan occur readily, leading to formation of disulfide linkages. Variousoxidizing agents can lead to such oxidative coupling. The oxygen in theair can in some cases lead to such oxidative coupling during storage ofthe polythiol. It is believed that a possible mechanism for theoxidative coupling of thiol groups involves the formation of thiylradicals, followed by coupling of said thiyl radicals, to form disulfidelinkage. It is further believed that formation of disulfide linkage canoccur under conditions that can lead to the formation of thiyl radical,including but not limited to reaction conditions involving free radicalinitiation. The polythiols can include species containing disulfidelinkages formed during storage.

The polythiols for use as compound (b) in the preparation of thepolymerizable composition of the present invention can also includespecies containing disulfide linkages formed during synthesis of thepolythiol.

In certain embodiments, the dithiol for use in the present invention,can include at least one dithiol represented by the following structuralformulas:

The sulfide-containing dithiols comprising 1,3-dithiolane (e.g.,formulas II and III) or 1,3-dithiane (e.g., formulas IV and V) can beprepared by reacting asym-dichloroacetone with dimercaptan, and thenreacting the reaction product with dimercaptoalkylsulfide, dimercaptanor mixtures thereof, as described in U.S. Pat. No. 7,009,032 B2.

Non-limiting examples of suitable dimercaptans for use in the reactionwith asym-dichloroacetone can include but are not limited to materialsrepresented by the following formula:

wherein Y can represent CH₂ or (CH₂—S—CH₂), and n can be an integer from0 to 5. The dimercaptan for reaction with asym-dichloroacetone in thepresent invention can be chosen from, for example, ethanedithiol,propanedithiol, and mixtures thereof.

The amount of asym-dichloroacetone and dimercaptan suitable for carryingout the above reaction can vary. For example, asym-dichloroacetone anddimercaptan can be present in the reaction mixture in an amount suchthat the molar ratio of dichloroacetone to dimercaptan can be from 1:1to 1:10.

Suitable temperatures for reacting asym-dichloroacetone with dimercaptancan vary, often ranging from 0 to 100° C.

Non-limiting examples of suitable dimercaptans for use in the reactionwith the reaction product of the asym-dichloroacetone and dimercaptan,can include but are not limited to materials represented by the abovegeneral formula VI, aromatic dimercaptans, cycloalkyl dimercaptans,heterocyclic dimercaptans, branched dimercaptans, and mixtures thereof.

Non-limiting examples of suitable dimercaptoalkylsulfides for use in thereaction with the reaction product of the asym-dichloroacetone anddimercaptan, can include materials represented by the following formula:

wherein X can represent O, S or Se, n can be an integer from 0 to 10, mcan be an integer from 0 to 10, p can be an integer from 1 to 10, q canbe an integer from 0 to 3, and with the proviso that (m+n) is an integerfrom 1 to 20.

Non-limiting examples of suitable dimercaptoalkylsulfides for use in thepresent invention can include branched dimercaptoalkylsulfides.

The amount of dimercaptan, dimercaptoalkylsulfide, or mixtures thereof,suitable for reacting with the reaction product of asym-dichloroacetoneand dimercaptan, can vary. Typically, dimercaptan,dimercaptoalkylsulfide, or a mixture thereof, can be present in thereaction mixture in an amount such that the equivalent ratio of reactionproduct to dimercaptan, dimercaptoalkylsulfide, or a mixture thereof,can be from 1:1.01 to 1:2. Moreover, suitable temperatures for carryingout this reaction can vary within the range of from 0 to 100° C.

The reaction of asym-dichloroacetone with dimercaptan can be carried outin the presence of an acid catalyst. The acid catalyst can be selectedfrom a wide variety known in the art, such as but not limited to Lewisacids and Bronsted acids. Non-limiting examples of suitable acidcatalysts can include those described in Ullmann's Encyclopedia ofIndustrial Chemistry, 5th Edition, 1992, Volume A21, pp. 673 to 674. Theacid catalyst is often chosen from boron trifluoride etherate, hydrogenchloride, toluenesulfonic acid, and mixtures thereof. The amount of acidcatalyst can vary from 0.01 to 10 percent by weight of the reactionmixture.

The reaction product of asym-dichloroacetone and dimercaptan canalternatively be reacted with dimercaptoalkylsulfide, dimercaptan ormixtures thereof, in the presence of a base. The base can be selectedfrom a wide variety known in the art, such as but not limited to Lewisbases and Bronsted bases. Non-limiting examples of suitable bases caninclude those described in Ullmann's Encyclopedia of IndustrialChemistry, 5th Edition, 1992, Volume A21, pp. 673 to 674. The base isoften sodium hydroxide. The amount of base can vary. Typically, asuitable equivalent ratio of base to reaction product of the firstreaction, can be from 1:1 to 10:1.

The reaction of asym-dichloroacetone with dimercaptan can be carried outin the presence of a solvent. The solvent can be selected from but isnot limited to organic solvents. Non-limiting examples of suitablesolvents can include but are not limited to chloroform, dichloromethane,1,2-dichloroethane, diethyl ether, benzene, toluene, acetic acid andmixtures thereof.

In another embodiment, the reaction product of asym-dichloroacetone anddimercaptan can be reacted with dimercaptoalkylsulfide, dimercaptan ormixtures thereof, with or without the presence of a solvent, wherein thesolvent can be selected from but is not limited to organic solvents.Non-limiting examples of suitable organic solvents can include alcoholssuch as but not limited to methanol, ethanol and propanol; aromatichydrocarbon solvents such as but not limited to benzene, toluene,xylene; ketones such as but not limited to methyl ethyl ketone; water,and mixtures thereof.

The reaction of asym-dichloroacetone with dimercaptan can also becarried out in the presence of a dehydrating reagent. The dehydratingreagent can be selected from a wide variety known in the art. Suitabledehydrating reagents for use in this reaction can include but are notlimited to magnesium sulfate. The amount of dehydrating reagent can varywidely according to the stoichiometry of the dehydrating reaction.

The polythiols for use as compound (b) can be prepared in certainnon-limiting embodiments by reacting2-methyl-2-dichloromethyl-1,3-dithiolane with dimercaptodiethylsulfideto produce dimercapto-1,3-dithiolane derivative of formula III.Alternatively, 2-methyl-2-dichloromethyl-1,3-dithiolane can be reactedwith 1,2-ethanedithiol to produce dimercapto-1,3-dithiolane derivativeof formula II. 2-methyl-2-dichloromethyl-1,3-dithiane can be reactedwith dimercaptodiethylsulfide to produce dimercapto-1,3-dithianederivative of formula V. Also, 2-methyl-2-dichloromethyl-1,3-dithianecan be reacted with 1,2-ethanedithiol to produce dimercapto-1,3-dithianederivative of formula IV.

Another non-limiting example of a dithiol suitable for use as thematerial (ii) can include at least one dithiol oligomer prepared byreacting dichloro derivative with dimercaptoalkylsulfide as follows:

wherein R can represent CH₃, CH₃CO, C1 to C10 alkyl, cycloalkyl, arylalkyl, or alkyl-CO; Y can represent C1 to C10 alkyl, cycloalkyl, C6 toC14 aryl, (CH₂)_(p)(S)_(m)(CH₂)_(q), (CH₂)_(p)(Se)_(m)(CH₂)_(q),(CH₂)_(p)(Te)_(m)(CH₂)_(q) wherein m can be an integer from 1 to 5 and,p and q can each be an integer from 1 to 10; n can be an integer from 1to 20; and x can be an integer from 0 to 10.

The reaction of dichloro derivative with dimercaptoalkylsufide can becarried out in the presence of a base. Suitable bases include any knownto those skilled in the art in addition to those disclosed above.

The reaction of dichloro derivative with dimercaptoalkylsulfide may becarried out in the presence of a phase transfer catalyst. Suitable phasetransfer catalysts for use in the present invention are known andvaried. Non-limiting examples can include but are not limited totetraalkylammonium salts and tetraalkylphosphonium salts. This reactionis often carried out in the presence of tetrabutylphosphonium bromide asphase transfer catalyst. The amount of phase transfer catalyst can varywidely, from 0 to 50 equivalent percent, or from 0 to 10 equivalentpercent, or from 0 to 5 equivalent percent, relative to thedimercaptosulfide reactants.

The polythiols for use as compound (b) may further contain hydroxylfunctionality. Non-limiting examples of suitable materials having bothhydroxyl and multiple (more than one) thiol groups can include but arenot limited to glycerin bis(2-mercaptoacetate), glycerinbis(3-mercaptopropionate), 1,3-dimercapto-2-propanol,2,3-dimercapto-1-propanol, trimethylolpropane bis(2-mercaptoacetate),trimethylolpropane bis(3-mercaptopropionate), pentaerythritolbis(2-mercaptoacetate), pentaerythritol tris(2-mercaptoacetate),pentaerythritol bis(3-mercaptopropionate), pentaerythritoltris(3-mercaptopropionate), and mixtures thereof.

In addition to dithiols disclosed above, particular examples of suitabledithiols can include 1,2-ethanedithiol, 1,2-propanedithiol,1,3-propanedithiol, 1,3-butanedithiol, 1,4-butanedithiol,2,3-butanedithiol, 1,3-pentanedithiol, 1,5-pentanedithiol,1,6-hexanedithiol, 1,3-dimercapto-3-methylbutane, dipentenedimercaptan,ethylcyclohexyldithiol (ECHDT), dimercaptodiethylsulfide (DMDS),methyl-substituted dimercaptodiethylsulfide, dimethyl-substituteddimercaptodiethylsulfide, 3,6-dioxa-1,8-octanedithiol,1,5-dimercapto-3-oxapentane, 2,5-dimercaptomethyl-1,4-dithiane (DMMD),ethylene glycol di(2-mercaptoacetate), ethylene glycoldi(3-mercaptopropionate), and mixtures thereof.

Suitable trifunctional or higher-functional polythiols for use ascompound (b) can be selected from a wide variety known in the art.Non-limiting examples can include pentaerythritoltetrakis(2-mercaptoacetate), pentaerythritoltetrakis(3-mercaptopropionate), trimethylolpropanetris(2-mercaptoacetate), trimethylolpropane tris(3-mercaptopropionate),2,3(bis((2-mercaptoethyl)thio)-1-propanethiol (GST), and/or thioglycerolbis(2-mercaptoacetate).

For example, the polythiol can be chosen from materials represented bythe following general formula,

wherein R₁ and R₂ can each be independently chosen from straight orbranched chain alkylene, cyclic alkylene, phenylene and C₁-C₉ alkylsubstituted phenylene. Non-limiting examples of straight or branchedchain alkylene can include methylene, ethylene, 1,3-propylene,1,2-propylene, 1,4-butylene, 1,2-butylene, pentylene, hexylene,heptylene, octylene, nonylene, decylene, undecylene, octadecylene andicosylene. Non-limiting examples of cyclic alkylenes can includecyclopentylene, cyclohexylene, cycloheptylene, cyclooctylene, andalkyl-substituted derivatives thereof. The divalent linking groups R₁and R₂ can be chosen from methylene, ethylene, phenylene, andalkyl-substituted phenylene, such as methyl, ethyl, propyl, isopropyland nonyl substituted phenylene.

In particular embodiments, a polythiol may be prepared by reactingtogether (1) any of the dithiols mentioned above, and (2) a compoundhaving at least two double bonds (for example, a diene) or a compoundcontaining a triple bond.

The compound (2) having triple bond functionality may comprise any knownalkyne, for example, propargyl alcohol, propargyl chloride, propargylbromide, propargyl acetate, propargyl propionate, propargyl benzoate,phenyl acetylene, phenyl propargyl sulfide, 1,4-dichloro-2-butyne,2-butyne-1,4-diol, 3-butyne-2-ol, 2-pentyne, 1-hexyne, 2-hexyne,3-hexyne, 3-hexyne-2,5-diol, and/or mixtures thereof.

The compound (2) having at least two double bonds can be chosen fromnon-cyclic dienes, including straight chain and/or branched aliphaticnon-cyclic dienes, non-aromatic ring-containing dienes, includingnon-aromatic ring-containing dienes wherein the double bonds can becontained within the ring or not contained within the ring or anycombination thereof, and wherein the non-aromatic ring-containing dienescan contain non-aromatic monocyclic groups or non-aromatic polycyclicgroups or combinations thereof; aromatic ring-containing dienes; orheterocyclic ring-containing dienes; or dienes containing anycombination of such non-cyclic and/or cyclic groups. The dienes canoptionally contain thioether, disulfide, polysulfide, sulfone, ester,thioester, carbonate, thiocarbonate, urethane, or thiourethane linkages,or halogen substituents, or combinations thereof; with the proviso thatthe dienes contain double bonds capable of undergoing reaction with SHgroups of a polythiol, and forming covalent C—S bonds. Often thecompound (2) having at least two double bonds comprises a mixture ofdienes that are different from one another.

The compound (2) having at least two double bonds may comprise acyclicnon-conjugated dienes, acyclic polyvinyl ethers, allyl-(meth)acrylatesvinyl-(meth)acrylates, di(meth)acrylate esters of diols,di(meth)acrylate esters of dithiols, di(meth)acrylate esters ofpoly(alkyleneglycol) diols, monocyclic non-aromatic dienes, polycyclicnon-aromatic dienes, aromatic ring-containing dienes, diallyl esters ofaromatic ring dicarboxylic acids, divinyl esters of aromatic ringdicarboxylic acids, and/or mixtures thereof.

Non-limiting examples of acyclic non-conjugated dienes can include thoserepresented by the following general formula:

wherein R can represent C1 to C30 linear or branched divalent saturatedalkylene radical, or C2 to C30 divalent organic radical including groupssuch as but not limited to those containing ether, thioether, ester,thioester, ketone, polysulfide, sulfone and combinations thereof. Theacyclic non-conjugated dienes can be selected from 1,5-hexadiene,1,6-heptadiene, 1,7-octadiene and mixtures thereof.

Non-limiting examples of suitable acyclic polyvinyl ethers can includethose represented by the following structural formula:

CH₂═CH—O—(—R2-O—)_(m)—CH═CH₂

wherein R2 can be C2 to C6 n-alkylene, C3 to C6 branched alkylene group,or —[(CH₂—)_(p)—O—]_(q)—(—CH2-)_(r)—, m can be a rational number from 0to 10, often 2; p can be an integer from 2 to 6, q can be an integerfrom 1 to 5 and r can be an integer from 2 to 10.

Non-limiting examples of suitable polyvinyl ether monomers for use caninclude divinyl ether monomers, such as ethylene glycol divinyl ether,diethylene glycol divinyl ether, triethyleneglycol divinyl ether, andmixtures thereof.

Di(meth)acrylate esters of linear diols can include ethanedioldi(meth)acrylate, 1,3-propanediol dimethacrylate, 1,2-propanedioldi(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,3-butanedioldi(meth)acrylate, 1,2-butanediol di(meth)acrylate, and mixtures thereof.

Di(meth)acrylate esters of dithiols can include, for example,di(meth)acrylate of 1,2-ethanedithiol including oligomers thereof,di(meth)acrylate of dimercaptodiethyl sulfide (i.e.,2,2′-thioethanedthiol di(meth)acrylate) including oligomers thereof,di(meth)acrylate of 3,6-dioxa-1,8-octanedithiol including oligomersthereof, di(meth)acrylate of 2-mercaptoethyl ether including oligomersthereof, di(meth)acrylate of 4,4′-thiodibenzenethiol, and mixturesthereof.

Further non-limiting examples of suitable dienes can include monocyclicaliphatic dienes such as those represented by the following structuralformula:

wherein X and Y each independently can represent C1-10 divalentsaturated alkylene radical; or C1-5 divalent saturated alkylene radical,containing at least one element selected from the group of sulfur,oxygen and silicon in addition to the carbon and hydrogen atoms; and R1can represent H, or C1-C10 alkyl; and

wherein X and R1 can be as defined above and R2 can represent C2-C10alkenyl. The monocyclic aliphatic dienes can include 1,4-cyclohexadiene,4-vinyl-1-cyclohexene, dipentene and terpinene.

Non-limiting examples of polycyclic aliphatic dienes can include5-vinyl-2-norbornene; 2,5-norbornadiene; dicyclopentadiene and mixturesthereof.

Non-limiting examples of aromatic ring-containing dienes can includethose represented by the following structural formula:

wherein R4 can represent hydrogen or methyl. Aromatic ring-containingdienes can include monomers such as diisopropenyl benzene, divinylbenzene and mixtures thereof.

Examples of diallyl esters of aromatic ring dicarboxylic acids caninclude but are not limited to those represented by the followingstructural formula:

wherein m and n each independently can be an integer from 0 to 5. Thediallyl esters of aromatic ring dicarboxylic acids can include o-diallylphthalate, m-diallyl phthalate, p-diallyl phthalate and mixturesthereof.

Often, the compound (2) having at least two double bonds comprises5-vinyl-2-norbornene, ethylene glycol divinyl ether, diethylene glycoldivinyl ether, triethylene glycol divinyl ether, butane diol divinylether, vinylcyclohexene, 4-vinyl-1-cyclohexene, dipentene, terpinene,dicyclopentadiene, cyclododecadiene, cyclooctadiene,2-cyclopenten-1-yl-ether, 2,5-norbornadiene, divinylbenzene including1,3-divinylbenzene, 1,2-divinylbenzene, and 1,4-divinylbenzene,diisopropenylbenzene including 1,3-diisopropenylbenzene,1,2-diisopropenylbenzene, and 1,4-diisopropenylbenzene, allyl(meth)acrylate, ethanediol di(meth)acrylate, 1,3-propanedioldi(meth)acrylate, 1,2-propanediol di(meth)acrylate, 1,3-butanedioldi(meth)acrylate, 1,2-butanediol di(meth)acrylate, ethylene glycoldi(meth)acrylate, diethylene glycol di(meth)acrylate,dimercaptodiethylsulfide di(meth)acrylate, 1,2-ethanedithioldi(meth)acrylate, and/or mixtures thereof.

Other non-limiting examples of suitable di(meth)acrylate monomers caninclude ethylene glycol di(meth)acrylate, 1,3-butylene glycoldi(meth)acrylate, 1,4-butanediol di(meth)acrylate,2,3-dimethyl-1,3-propanediol di(meth)acrylate, 1,6-hexanedioldi(meth)acrylate, propylene glycol di(meth)acrylate, dipropylene glycoldi(meth)acrylate, tripropylene glycol di(meth)acrylate, tetrapropyleneglycol di(meth)acrylate, ethoxylated hexanediol di(meth)acrylate,propoxylated hexanediol di(meth)acrylate, neopentyl glycoldi(meth)acrylate, alkoxylated neopentyl glycol di(meth)acrylate,hexylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate,polyethylene glycol di(meth)acrylate, thiodiethyleneglycoldi(meth)acrylate, trimethylene glycol di(meth)acrylate, triethyleneglycol di(meth)acrylate, alkoxylated hexanediol di(meth)acrylate,alkoxylated neopentyl glycol di(meth)acrylate, pentanedioldi(meth)acrylate, cyclohexane dimethanol di(meth)acrylate, andethoxylated bis-phenol A di(meth)acrylate.

As noted above, the reactants (a) and (b) are reacted together via aMichael addition reaction. Typically the reactants are combined with themonomer (a) in stoichiometric excess. For example, the molar ratio ofthe polythiol compound (b) to the monomer (a) is usually 1:2.

The reactants are reacted in the presence of a base to form the epoxidefunctional reaction product. Suitable bases include Lewis bases such as1,4-diazabicyclo[2.2.2]octane (DABCO); tertiary amines, phosphines, andthe like.

In accordance with the present invention, a thioepoxide functionalpolymerizable composition may be prepared by reacting the epoxidefunctional reaction product described above with thiourea. In theexemplary reaction scheme below, an epoxide functional Michael additionreaction product of glycidyl methacrylate andbis(2-mercaptoethyl)sulfide is reacted with thiourea:

Due to the high reactivity of thioepoxide groups in the presence ofbases, it is advisable to add the thiourea to the epoxide functionalreaction product after the Michael addition reaction of the epoxidefunctional monomer having ethylenically unsaturated groups and thepolythiol, in order to avoid formation of unwanted polymeric by-productsand to ensure formation of the thioepoxide functional polymerizablecomposition.

In a further embodiment of the present invention, an additionalpolymerizable composition may be prepared, comprising a reaction productof (a) a monomer composition comprising at least one ethylenicallyunsaturated (meth)acrylate functional monomer having a thioepoxidefunctional group and (b) the thioepoxide functional polymerizablecomposition described above. Examples of such monomers (a) includethioglycidyl methacrylate.

In such a polymerizable composition, the monomer composition (a) mayfurther comprise at least one different polymerizable ethylenicallyunsaturated monomer. Ethylenically unsaturated groups include(meth)acryloyl, allyl, and/or vinyl groups. Useful alkyl esters ofacrylic acid or methacrylic acid include aliphatic alkyl esterscontaining from 1 to 30, and preferably 4 to 18 carbon atoms in thealkyl group, which may be linear, branched, cyclic, and/or substituted.Representative alkyl groups include but are not limited to methyl,ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl,pentyl, neopentyl, hexyl, heptyl, octyl, nonyl, decyl, and structuralisomers thereof. Representative cycloalkyl groups include but are notlimited to cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, andcyclooctyl substituents. Representative poly-fused-ring cycloalkylgroups include but are not limited to decahydronaphthalenyl,tetradecahydroanthracenyl, and tetradecahydrophenanthrenyl.Representative polycyclicalkyl groups include but are not limited to,bicyclo[2.2.1]heptanyl (norbornyl), and bicyclo[2.2.2]octanyl.Representative heterocycloalkyl groups include but are not limited totetrahydrofuranyl, tetrahydropyranyl and piperidinyl, including but notlimited to piperidin-4-yl. Representative polycyclicheterocycloalkylgroups include but are not limited to, 7-thiabicyclo[2.2.1]heptanyl,7-oxabicyclo[2.2.1]heptanyl, and 7-azabicyclo[2.2.1]heptanyl.Representative aralkyl groups include but are not limited to benzyl, andphenethyl. Examples of monomers having a single ethylenicallyunsaturated radically polymerizable group that can be present in themonomer composition (a) of the polymerizable compositions of the presentinvention include, but are not limited to: acrylic acid; methacrylicacid; esters of acrylic acid such as methyl or ethyl acrylate and2-hydroxyethyl acrylate; esters of methacrylic acid, such as methyl orethyl methacrylate, phenoxyethyl methacrylate, isobornyl methacrylate,cyclohexyl methacrylate and 2-hydroxyethyl methacrylate; allyl esters,e.g., allyl benzoate; allyl carbonates, e.g., phenyl allyl carbonate;vinyl esters such as vinyl acetate; styrene; and vinyl chloride. In someembodiments, the monoethylenically unsaturated monomers include methylmethacrylate, isobornyl methacrylate, phenoxyethyl methacrylate,cyclohexyl methacrylate, styrene and mixtures thereof. Monomers havingmore than one ethylenically unsaturated group, such as divinyl benzene(DVB), may also be used in the monomer composition (a). Theethylenically unsaturated monomer(s), when used, is typically present inan amount of from 1 percent by weight to 60 percent by weight, based onthe total monomer weight of the polymerizable composition, such as from3 percent by weight to 55 percent by weight, or from 20 to 45 percent byweight, based on the total monomer weight of the polymerizablecomposition.

In this embodiment, the monomer composition (a) is typically present inthe polymerizable composition of the present invention in an amount of25 to 90 percent by weight, such as 25 to 75 percent by weight, or 50 to60 percent by weight based on the total weight of resin solids in thepolymerizable composition, while the thioepoxide functional,polymerizable composition (b) is typically present in an amount of 10 to75 percent by weight, such as 25 to 75 percent by weight, or 40 to 50percent by weight based on the total weight of resin solids in thepolymerizable composition.

The polymerizable compositions described above may be used to prepareoptical articles demonstrating high refractive indices. In oneembodiment of the present invention, a method of preparing an opticalarticle comprises:

(1) reacting together:

(a) a monomer comprising at least one ethylenically unsaturated esterfunctional monomer having an epoxide functional group; and

(b) a compound having two or more thiol groups;

wherein the reactants (a) and (b) are reacted via a Michael additionreaction in the presence of a base to form an epoxide functionalreaction product;(2) reacting the epoxide functional reaction product formed in step (1)with thiourea to form a thioepoxide functional, polymerizablecomposition;(3) mixing the thioepoxide functional, polymerizable composition formedin step (2) with:

(a) a polymerizable composition comprising at least one ethylenicallyunsaturated (meth)acrylate functional monomer having a thioepoxidefunctional group;

(b) an addition polymerization initiator; and

(c) a catalyst to form a reaction mixture;

(4) introducing the reaction mixture formed in step (3) to a mold of adesired shape at a temperature and for a time sufficient to form apolymerizate; and(5) releasing the polymerizate from the mold to yield an opticalarticle.

Steps (1) and (2) are described in detail above. In step (3), a reactionmixture is prepared by mixing the thioepoxide functional, polymerizablecomposition formed in step (2) with a polymerizable compositioncomprising at least one ethylenically unsaturated (meth)acrylatefunctional monomer having a thioepoxide functional group, an additionpolymerization initiator, and a catalyst to form a reaction mixture.

Suitable addition polymerization initiators include peroxy typeinitiators known in the art. Azo type initiators should be avoidedimmediately prior to molding of the polymerizable composition in orderto avoid appearance problems caused by gas evolution during reaction.

The polymerizable composition used in step (3) may comprise a prepolymerhaving a a viscosity of 50 to 500 centipoise measured at 25° C. Theviscosity may be controlled by careful addition of polymerizationinitiator. In the making of the prepolymer, any conventionalpolymerization initiator may be used including azo initiators; in fact,azo initiators are recommended for the prepolymerization. However, careshould be taken to remove azo initiators from the prepolymer prior tomolding for reasons noted above. The prepolymer may be prepared bypolymerizing an ethylenically unsaturated (meth)acrylate functionalmonomer having a thioepoxide functional group. Optionally, at least onedifferent polymerizable ethylenically unsaturated monomer, including anyof those disclosed above such as styrene, may be polymerized with thethioepoxide functional monomer.

The catalyst used in step (3) effects or promotes reaction between thebeta-epithiopropyl (thioepoxide) functional groups. The catalyst ispresent in an amount at least sufficient to effect reaction among thebeta-epithiopropyl functional groups in the polymerizable composition,such that the beta-epithiopropyl functional groups react with each otherin a chemical reaction such as a polymerization reaction.

Suitable catalysts may include one or more of: phosphines; quaternaryphosphonium salts; 1,4-diazabicyclo[2.2.2]octane, also known as1,4-diazabicyclo[2.2.2]octane or triethylenediamine; other aminecatalysts such as amines having a heterocyclic ring; quaternary ammoniumsalts; tertiary sulfonium salts; secondary iodonium salts; borontrihalides and complexes thereof; organic acids and esters thereof; andmetal halides.

Examples of amines having a heterocyclic ring include imidazoles such asimidazole, N-methylimidazole, N-methyl-2-mercaptoimidazole,2-methylimidazole, 4-methylimidazole, N-ethylimidazole,2-ethylimidazole, 4-ethylimidazole, N-butylimidazole, 2-butylimidazole.N-undecylimidazole, 2-undecylimidazole, N-phenylimidazole,2-phenylimidazole, N-benzylimidazole, 2-benzylimidazole,1-benzyl-2-methylimidazole, N-(2′-cyanoethyl)-2-methylimidazole,N-(2′-cyanoethyl)-2-undecylimidazole,N-(2′-cyanoethyl)-2-phenylimidazole,3,3-bis(2-ethyl-4-methylimidazolyl)methane, adducts of alkylimidazoleand isocyanuric acid, condensates of alkylimidazole and formaldehyde,and the like; and amidines such as 1,8-diazabicyclo[5.4.0]undecene,1,5-diazabicyclo[4.3.0]nonene,5,6-dibutylamino-1,8-diazabicyclo[5.4.0]undecene, and the like.

Specific examples of suitable phosphines include trimethylphosphine,triethylphosphine, triisopropylphosphine, tributylphosphine,tricyclohexylphosphine, trioctylphosphine, triphenylphosphine,tribenzylphosphine, tris(2-methylphenyl)phosphine,tris(3-methylphenyl)phosphine, tris(4-methylphenyl)phosphine,tris(diethylamino)phosphine, dimethylphenylphosphine,diethylphenylphosphine, dicyclohexylphenylphosphine,diethylphenylphosphine, dicyclohexylphenylphosphine,ethyldiphenylphosphine, diphenylcyclohexylphosphine,chlorodiphenylphosphine, and the like.

Examples of quaternary ammonium salts that may be used as a catalystinclude tetramethylammoniumchloride, tetramethylammoniumbromide,tetramethylammoniumacetate, tetraethylammoniumchloride,tetraethylammoniumbromide, tetraethylammoniumacetate,tetra-n-butylammoniumfluoride, tetra-n-butylammoniumchloride,tetra-n-butylammoniumbromide, tetra-n-butylammoniumiodide,tetra-n-butylammoniumacetate, tetra-n-butylammoniumborohydride,tetra-n-butylammoniumhexafluorophosphite,tetra-n-butylammoniumhydrogensulphite,tetra-n-butylammoniumtetrafluoroborate,tetra-n-butylammoniumtetraphenylborate,tetra-n-butylammoniumparatoluenesulfonate,tetra-n-hexylammoniumchloride, tetra-n-hexylammoniumbromide,tetra-n-hexylammoniumacetate, tetra-n-octylammoniumchloride,tetra-n-octylammoniumbromide, tetra-n-octylammoniumacetate,trimethyl-n-octylammoniumchloride, trimethylbenzylammoniumchloride,trimethylbenzylammoniumbromide, triethyl-n-octylammoniumchloride,triethylbenzylammoniumchloride, triethylbenzylammoniumbromide,tri-n-butyl-n-octylammoniumchloride, tri-n-butylbenzylammoniumfluoride,tri-n-butylbenzylammoniumchloride, tri-n-butylbenzylammoniumbromide,tri-n-butylbenzylammoniumiodide, methyltriphenylammoniumchloride,methyltriphenylammoniumbromide, ethyltriphenylammoniumchloride,ethyltriphenylammoniumbromide, n-butyltriphenylammoniumchloride,n-butyltriphenylammoniumbromide, 1-methylpyridiniumbromide,1-ethylpyridiniumbromide, 1-n-butylpyridiniumbromide,1-n-hexylpyndiniumbromide, 1-n-octylpyridiniumbromide,1-n-dodecylpyridiniumbromide, 1-phenylpyridiniumbromide,1-methylpicoliniumbromide, 1-ethylpicoliniumbromide,1-n-butylpicoliniumbromide, 1-n-hexylpicoliniumbromide,1-n-octylpicoliniumbromide, 1-n-dodecylpicoliniumbromide,1-phenylpicoliniumbromide, and the like.

Specific examples of suitable quaternary phosphonium salts includetetramethylphosphoniumchloride, tetramethylphosphoniumbromide,tetraethylphosphoniumchloride, tetraethylphosphoniumbromide,tetra-n-butylphosphoniumchloride, tetra-n-butylphosphoniumbromide,tetra-n-butylphosphoniumiodide, tetra-n-hexylphosphoniumbromide,tetra-n-octylphosphoniumbromide, methyltriphenylphosphoniumbromide,methyltriphenylphosphoniumiodide, ethyltriphenylphosphoniumbromide,ethyltriphenylphosphoniumiodide, n-butyltriphenylphosphoniumbromide,n-butyltriphenylphosphoniumiodide, n-hexyltriphenylphosphoniumbromide,n-octyltriphenylphosphoniumbromide, tetraphenylphosphoniumbromide,tetrakishydroxymethylphosphoniumchloride,tetrakishydroxymethylphosphoniumbromide,tetrakishydroxyethylphosphoniumchloride,tetrakishydroxybutylphosphoniumchloride, and the like.

Specific examples of the tertiary sulfonium salts includetrimethylsulfoniumbromide, triethylsulfoniumbromide,tri-n-butylsulfoniumchloride, tri-n-butylsulfoniumbromide,tri-n-butylsulfoniumiodide, tri-n-butylsulfoniumtetrafluoroborate,tri-n-hexylsulfoniumbromide, tri-n-octylsulfoniumbromide,triphenylsulfoniumchloride, triphenylsulfoniumbromide,triphenylsulfoniumiodide, and the like.

Suitable secondary iodonium salts include diphenyliodoniumchloride,diphenyliodoniumbromide, diphenyliodoniumiodide, and the like.

Specific examples of the boron trihalides and complexes thereof includeboron trifluoride, boron trifluoride-ethylether complex, borontrifluoride-n-butylether complex, boron trifluoride-phenol complex,boron trifluoride-ethylamine complex, boron trifluoride-piperidinecomplex, boron trifluoride-acetic acid complex, borontrifluoride-triethanolamine complex, boron trifluoride-ammonia complex,and the like.

Examples of catalytic organic acids and esters thereof include sulfonicacid, carboxylic acid, and esters thereof. Specific examples thereofinclude methanesulfonic acid, trifluoromethanesulfonic acid,benzenesulfonic acid, p-toluenesulfonic acid, 10-chamfer sulfonic acid,and methyl and ethylesters thereof.

Specific examples of metal halides include zinc chloride, iron chloride,aluminum chloride, tin chloride, titanium chloride, methylaluminumdichloride, ethylaluminum dichloride, dimethylaluminum chloride, anddiethylaluminum chloride.

The amount of catalyst present in the reaction mixture is sufficient toeffect reaction between the beta-epithiopropyl functional groups in thereaction mixture. The amount of the catalyst is typically 0.001 to 3% byweight, such as 0.005 to 2% by weight, based on the total weight ofresin solids in the reaction mixture.

In certain embodiments of the present invention, additional reactantsmay be added to the reaction mixture immediately prior to introducingthe reaction mixture to the mold. For example, at least one differentpolymerizable ethylenically unsaturated monomer, including any of thosedisclosed above, may be added to the reaction mixture. In addition oralternatively, at least one compound having two or morebeta-epithiopropyl functional groups but no polymerizable ethylenicallyunsaturated groups may be added to the reaction mixture. Examples ofsuch compounds include bis(beta-epithiopropyl)sulfide,bis(beta-epithiopropyl)disulfide, andbis(beta-epithiopropyloxyphenyl)propane.Bis(beta-epithiopropyloxyphenyl)propane, also called Bisphenol Adithioglycidylether, may be formed as a reaction product of a reactioncomposition comprising 2,2-bis(4-glycidyloxyphenyl)propane and thiourea.The 2,2-bis(4-glycidyloxyphenyl)propane may be formed as a reactionproduct of a reaction composition comprising2,2-bis(4-hydroxyphenyl)propane (Bisphenol A) and epichlorohydrin.

The thermal cure cycle used to cure the polymerizable compositions ofthe present invention, with some embodiments, involves heating thepolymerizable composition in the presence of the initiator from roomtemperature up to 50° C. to 150° C., over a period of from 2 hours to 48hours, or from 55° C. up to 90° C. or 100° C. over a period of from 12to 24 hours, or from 65° C. up to 115° C. or 125° C. over a period offrom 12 to 24 hours.

Polymerization of the reaction mixtures of the present invention resultsin the formation of a polymerizate, which can be in the form of a shapedarticle. Polymerizates obtained from polymerization of the polymerizablecompositions of the present invention are solid, and with someembodiments, transparent. Transparent polymerizates prepared from thepolymerizable compositions of the present invention, can be used inoptical or ophthalmic applications.

Polymerizates prepared from the polymerizable compositions of thepresent invention can be used to form solid articles such as opticalelement(s) or device(s). As used herein the term “optical” meanspertaining to or associated with light and/or vision. For example, theoptical element or device can comprise ophthalmic elements and devices,display elements and devices, windows, mirrors, and/or active andpassive liquid crystal cell elements and devices. As used herein theterm “ophthalmic” means pertaining to or associated with the eye andvision. Non-limiting examples of ophthalmic elements include correctiveand non-corrective lenses, including single vision or multi-visionlenses, which may be either segmented or non-segmented multi-visionlenses (such as, but not limited to, bifocal lenses, trifocal lenses andprogressive lenses), as well as other elements used to correct, protect,or enhance (cosmetically or otherwise) vision, including withoutlimitation, contact lenses, intra-ocular lenses, magnifying lenses, andprotective lenses or visors. As used herein the term “display” means thevisible or machine-readable representation of information in words,numbers, symbols, designs or drawings. Non-limiting examples of displayelements and devices include screens, monitors, and security elements,such as security marks. As used herein the term “window” means anaperture adapted to permit the transmission of radiation there-through.Non-limiting examples of windows include automotive and aircrafttransparencies, filters, shutters, and optical switches. As used hereinthe term “mirror” means a surface that specularly reflects a largefraction of incident light.

In step (4) of the method of the present invention, the reaction mixturemay be introduced into a mold of any desired shape at a temperature andfor a time to form a polymerizate. The second reaction mixture typicallyundergoes an exothermic reaction, and after mixing it is introduced,usually by injection, into a mold. The temperature of the reactionmixture as it is introduced into the mold is usually up to 130° C.,often up to 120° C. The reaction mixture is held in the mold at atemperature and for a time sufficient to essentially cure the reactionmixture and form a molded optical article. The mold may have any shapedesired for the final product as noted above. It is typically a lensmold; often a mold for an ophthalmic lens. The molded article may thenbe released from the mold. Optical articles prepared by the process ofthe present invention demonstrate high yield, high transparency, verylow haze, low flow lines and low inclusions. Moreover, the opticalarticles prepared by the method of the present invention demonstrate arefractive index of at least 1.57.

In an embodiment of the present invention wherein the optical article isa lens, the reaction mixture, which can be optionally degassed, can beintroduced into a mold and the mold can be heated (i.e., using a thermalcure cycle) using a variety of conventional techniques known in the art.The thermal cure cycle can vary depending on the reactivity and molarratio of the reactants, and the presence of catalyst(s). In particularembodiments for lenses, the thermal cure cycle can include heating themixture from room temperature to a temperature of 200° C. over a periodof from 0.5 hours to 120 hours; or from 80 to 150° C. for a period offrom 5 hours to 72 hours.

In a particular embodiment of the present invention, the methodcomprises the following steps:

-   -   (1) reacting together.    -   (a) a monomer comprising at least one ethylenically unsaturated        ester functional monomer having an epoxide functional group; and    -   (b) a compound having two or more thiol groups;        wherein the reactant (a) is present in stoichiometric excess and        the reactants (a) and (b) are reacted via a Michael addition        reaction in the presence of a base to form a product mixture        comprising an epoxide functional reaction product and excess        monomer (a);    -   (2) reacting the product mixture formed in step (1) with        thiourea to form a thioepoxide functional, polymerizable        composition;    -   (3) preparing a prepolymer reactant mixture by:    -   (i) mixing the thioepoxide functional, polymerizable composition        formed in step (2) with:        -   (a) a first polymerizable composition comprising at least            one ethylenically unsaturated monomer; and        -   (b) an azo addition polymerization initiator to form a            reaction mixture; and    -   (ii) allowing ethylenically unsaturated groups in the reaction        mixture formed in (i) to polymerize to form a prepolymer having        a threshold viscosity of 50 to 500 centipoise measured at 25°        C., wherein the azo addition polymerization initiator is present        in an amount sufficient only to achieve the threshold viscosity;    -   (4) mixing the prepolymer reactant mixture formed in step (3)        with:        -   (a) an initiator package that is essentially free of azo            initiators; and        -   (b) a second polymerizable composition comprising at least            one ethylenically unsaturated monomer having two or more            ethylenically unsaturated groups to form a moldable            composition;    -   (5) introducing the moldable composition formed in step (4) to a        mold of a desired shape at a temperature and for a time        sufficient to form a polymerizate;    -   (6) releasing the polymerizate from the mold to yield an optical        article.

In this embodiment of the present invention, in step (1), the equivalentratio of ethylenically unsaturated groups in the monomer (a) to thiolgroups in the compound (b) is often greater than 1.1:1, and can be anyratio up to 99:1, such as 2:1, 5:1, 10:1, etc.

In step (4) of this embodiment, the initiator package (a) typicallycomprises peroxy functional initiators and a catalyst for ring-openingpolymerization. The ethylenically unsaturated monomer having two or moreethylenically unsaturated groups may be any of those disclosed above; itis most often divinylbenzene.

Optical articles prepared using the polymerizable compositions of thepresent invention typically demonstrate high refractive indices, such asat least 1.57, and high ABBE numbers, such as at least 35.

The present invention is more particularly described in the followingexamples, which are intended to be illustrative only, since numerousmodifications and variations therein will be apparent to those skilledin the art. Unless otherwise specified, all parts and percentages are byweight.

EXAMPLES

The analytical procedures used to determine the properties of theprepared materials and the abbreviations used herein are described inPart 1. Part 2 describes the preparation of Comparative Example 1(thioglycidyl methacrylate). Part 3 describes the preparation ofExamples 1 to 11. Part 4 describes the procedure used for preparingcasting a polymer sample of Examples 1, 2, 8-11 and CE-1 and theproperties of the polymerizates.

Part 1—Analytical Procedures

All ¹H NMR data was obtained using a Bruker spectrometer operating at anominal proton frequency of 500.13 MHz. All spectra were obtained usingCDCl₃ as the solvent.

All IR data were obtained using a Bruker FRA-106/s FT-Raman systemutilizing representative peaks at 1655-1616 cm⁻¹ to identify the C═Cbonds of styrene and the methacrylate, and peaks at 675-640 cm⁻¹ toidentify the C—S—C bonds of the thioepoxide.

The refractive index ((RI-(E-Line)) of polymer samples was measuredusing a Metricon Model 2010M prism coupler according to ASTM C1648-06.The refractive index of liquid samples was measured using an Atago DR-M2Abbe Refractometer at 546 nm (mercury e-line) and 20° C. in accordancewith ASTM-D1218-02 (2007).

The viscosity of the liquid samples was measured using Brookfield CAP2000+ viscometer using spindle #1 at 1000 RPM at 25° C. The viscosity isreported in centipoise (cP). The microindentation hardness or Fischermicrohardness (FMH), measured according to ISO 14577-07 using aFischerscope H-100SMC available from Fischer Technology, Inc. TheFischer microhardness of the polymerizates, ±3 N/mm², was measured at aload of 300 mN, following a load application of 0-300 mN in 15 s.

The Yellowness Index (YI) was measured using a HunterLab UltraSan PROaccording to ASTM E313-10. The path length for sheet samples was equalto the sample thickness (3 mm) and the path length for liquid sampleswas 2 cm.

The Glass Transition Temperature (Tg) was determined by DynamicMechanical Analysis according to ASTM E1640-09 and is reported in ° C.

In addition to the abbreviations provided above, in the examples below,the following abbreviations have the following meanings. If anabbreviation is not defined, it has its generally accepted meaning.

BPA-TDGE=bisphenol A dithioglycidyl ether

DABCO=diazabicyclooctane

DMDS=dimercaptodiethylsulfide

DVB=divinyl benzene

GMA=glycidyl methacrylate

GST=2,3-bis((2-mercaptoethyl)thio)-1-propanethiol

MMA=methyl methacrylate

PTMA=pentaerythritol tetrakis(2-mercaptoacetate)

TBPB=tetra butyl phosphonium bromide

TGMA=thioglycidyl methacrylate

Part 2—Preparation of Comparative Example 1 (CE-1) (TGMA)

A 5-L jacketed reactor was fitted with a mechanical stirrer, athermometer, and a condenser. The vessel was charged with GMA (508 g,3.58 mol), acetic anhydride (40.2 g, 0.39 mol), methanol (700 mL), andtoluene (700 mL) under a nitrogen atmosphere. The mixture was heated to40° C., and thiourea (300 g, 3.95 mol) was added in 50 g portions in 15minute intervals. During these additions, the temperature of thereaction was monitored to maintain a temperature range of 40° C.-50° C.After the final portion was added, the reaction was stirred at thistemperature for an additional hour after which TLC analysis (30%ethylacetate in hexanes) showed no remaining GMA. The reaction mixturewas poured into a 4-L separatory funnel and washed twice with 700 mLportions of dilute H₂SO₄ (1 weight percent in water) and then washedtwice with 700 mL portions of aqueous saturated sodium chloridesolution. The organic layer was separated, recovered and stabilized withMEHQ (4-methoxyphenol) (44 mg, 0.36 mmol), dried over magnesium sulfate,and concentrated under vacuum. Clear oil was obtained upon concentration(480 g). The purity of the resulting product was determined by NMR(97.5% TGMA with 2.5% GMA). ¹H NMR δ 1.95 (s, 3H), δ 2.29 (dd, 1H), δ2.53 (dd, 1H), δ 3.16 (p, 1H), δ 4.17 (dd, 1H), δ 4.25 (dd, 1H), δ 5.60(t, 1H), δ 6.15 (s, 1H). RI (E-line) was 1.509; and Abbe was 38.

Part 3—Preparation of Examples 1-11 Example 1 Prepolymerization of TGMA(50%) and Styrene (50%)

A 1-L round-bottom flask fitted with a condenser and a magnetic stir barwas charged with TGMA made according to the procedure of CE-1 (50 g,0.32 mol) and styrene (50 g, 0.48 mol) under a nitrogen atmosphere. Vazo67 (2,2′-azobis(2-methylbutyronitrile) (0.05 g, 0.26 mmol) was added andthen the reaction mixture was heated to between 105-110° C. in an oilbath. While heating, the viscosity of the reaction mixture at 25° C. wasmonitored every 15 minutes. After 1 hour at the above temperature thereaction reached a stable viscosity at which point the reaction mixturewas removed from the heat. It was allowed to cool to room temperaturewhile being exposed to air (in order to activate the MEHQ radicalinhibitor introduced through the TGMA). Upon cooling, the reactionproduct was homogeneous, clear, colorless oil (100 g) with a viscosityof 325 cP at 25° C. The product was stored at 4° C. FT-Raman spectrumshowed that 40% of the total polymerizable double bonds were convertedto polymer during the reaction. Of each monomer, 48% of the TGMA and 35%of the styrene were converted to polymers. RI (E-line) was 1.5487 andAbbe was 29.5.

Example 2 Prepolymerization of TGMA (60%) and Styrene (40%)

The procedure of Example 1 was followed except that the following in theamounts indicated were used: TGMA (300 g, 1.89 mol), styrene (200 g,1.92 mol), and Vazo 67, reported to be2,2′-azobis(2-methylbutyronitrile), (0.25 g, 1.3 mmol). Upon cooling thereaction product was homogeneous, clear, colorless oil (500 g) with aviscosity 210 cP at 25° C. The product was stored at 4° C. FT-Ramanspectrum showed that 28.5% of the total polymerizable double bonds wereconverted to polymer during the reaction. Of each monomer, 29% of theTGMA and 28% of the styrene were converted to polymers. RI (E-line)1.5434 and Abbe 30.9 were measured.

Example 3 Preparation of Michael adduct of DMDS and TGMA in a One PotProcess

A 5-L jacketed reactor was fitted with a mechanical stirrer, athermometer, and a condenser. The reactor was charged with GMA (300 g,2.11 mol) and DABCO, reported to be diazabicyclooctane, (240 mg,2.1×10⁻³ mol) under a nitrogen atmosphere. The resulting mixture wasthen cooled to 0° C. and DMDS, (160 g, 1.04 mol) was added slowly toensure no increase in temperature (1-mL per minute). After the DMDS wasadded, the reaction was stirred at 0° C. for two hours, and a titrationwith iodine showed no free thiol to be present. The reaction was treatedwith acetic anhydride (23 g, 0.23 mol) and allowed to warm to roomtemperature at which point the mixture was diluted with toluene (1 L)and methanol (1 L). The mixture was then heated to 40° C., and thiourea(180 g, 2.37 mol) was added in ≈50 g portions in 15 minute intervals.During these additions, the temperature of the reaction was monitored tomaintain a temperature range of 40° C.-50° C. After the final portionwas added, the reaction was stirred at this temperature for three hoursafter which TLC analysis (20% ethylacetate in hexanes) showed noremaining Michael adduct of DMDS with GMA. The reaction mixture waspoured into a 4-L separatory funnel. The reaction mixture was washedtwice with 800-mL portions of dilute H₂SO₄ (1 weight % in water). Themixture was then washed twice with 800-mL portions of saturated aqueoussodium chloride solution. The organic layer was separated, recovered anddried over magnesium sulfate and concentrated under vacuum. Clear oilwas obtained upon filtration through a 0.45 μm filter press (375 g).Purity of the obtained product was determined by NMR analysis to be 94%DMDS-TGMA Michael Adduct and 6% TGMA. The viscosity of the product was237 cP at 25° C. ¹H NMR: d 1.18 (d, 6H), d 2.19 (dd, 2H), d 2.45 (dd,2H), d 2.56 (dd, 2H), d 2.64 (m, 2H), d 2.66 (s, 8H), d 2.77 (dd, 2H), d3.05 (p, 2H), d 4.09 (dd, 4H). RI (E-line) was 1.5628 and Abbe was 40.5.

Example 4 Preparation of Michael Adduct of DMDS and TGMA in a One PotProcess

The procedure of Example 3 was followed except that the followingmaterials in the amounts indicated were used: GMA (420 g, 2.96 mol),DABCO (24 mg, 2.2×10⁻⁴ mol), DMDS, (33.5 g, 0.22 mol), acetic anhydride(33 g, 0.32 mol), toluene (1 L), methanol (1 L), and thiourea (250 g,3.29 mol). The recovered organic layer was stabilized with MEHQ (50 mg,0.4 mmol), dried over magnesium sulfate, and concentrated under vacuum.Clear oil was obtained upon concentration (417 g). NMR spectra wereconsistent with a mixture of the two components, thioglycidylmethacrylate and DMDS-TGMA Michael adduct (NMR spectra reported in CE-1and Example 3) in a 10:1 molar ratio. RI (E-line) was 1.5288 and Abbewas 39.5.

Example 5 Preparation of Michael Adduct of GST and TGMA in a One PotProcess

The procedure of Example 3 was followed except that the followingmaterials in the amounts indicated were used: GMA (300 g, 2.11 mol),DABCO (240 mg, 2.1×10⁻³ mol), GST (180 g, 0.69 mol), acetic anhydride(23 g, 0.23 mol), toluene (1 L), methanol (1 L), and thiourea (180 g,2.37 mol). Slightly hazy oil was obtained upon concentration (380 g).The viscosity of this product was 615 cP at 25° C. ¹H NMR: d 1.27 (d,9H), d 2.29 (d, 3H), d 2.54 (d, 3H), d 2.67 (dd, 3H), d 2.71 (m, 3H), d2.76 (s, 8H), d 2.88 (m, 3H), d 2.91 (m, 4H), d 3.00 (p, 1H), d 3.15 (p,3H), d 4.19 (dd, 6H). RI (E-line) was 1.5677 and Abbe was 39.7

Example 6 Preparation of Michael Adduct of GST and TGMA in a One PotProcess

The procedure of Example 3 was followed except that the followingmaterials in the amounts indicated were used: GMA (420 g, 2.95 mol),DABCO (45 mg, 4×10⁻⁴ mol), GST (35 g, 0.13 mol), toluene (1 L), methanol(1 L) and thiourea (250 g, 3.29 mol). The organic layer was stabilizedwith MEHQ (50 mg, 0.4 mmol), dried over magnesium sulfate, andconcentrated under vacuum. Clear oil was obtained upon concentration(412 g). NMR spectra of the sample are consistent with a mixture of TGMAand GST-TGMA Michael adduct (NMR spectra reported in CE-1 and Example 5)in a ratio of 94:6. The viscosity of this product was lower than 50 cPat 25° C. RI (E-line) was 1.5177 and Abbe was 38.9.

Example 7 Prepolymerization of a Mixture Containing TGMA, Example 5 andStyrene

A 500-mL round-bottom flask fitted with a condenser and a magnetic stirbar was charged material made according to the procedure of CE-1 (96 g),material made according to the procedure of Example 5 (24 g) and styrene(80 g) under a nitrogen atmosphere. Vazo 67 (0.10 g) was added and thereaction mixture was heated to between 105-110° C. in an oil bath. Whileheating, the viscosity of the reaction mixture at 25° C. was monitoredevery 15 minutes. After 1 hour at the above temperature range thereaction reached a stable viscosity at which point the reaction mixturewas removed from the heat. It was allowed to cool to room temperaturewhile being exposed to air (in order to activate the MEHQ radicalinhibitor in the TGMA). Upon cooling the reaction product washomogeneous, clear, colorless oil (200 g). The viscosity of the productwas 75 cP at 25° C. RI (E-line) was 1.5477 and Abbe was 30.8. Theresulting product was stored at 4° C.

Example 8 Prepolymerization of the Material Described in Example 6 (60%)and Styrene (40%)

A 500-mL round-bottom flask fitted with a condenser and a magnetic stirbar was charged with material made according to the procedure of Example6 (120 g) and styrene (80 g) under a nitrogen atmosphere. Vazo 67 (0.10g) was added and the reaction mixture was heated to between 105-110° C.in an oil bath. While heating, the viscosity of the reaction mixture at25° C. was monitored every 15 minutes. After 1 hour at the abovetemperature range the reaction reached a stable viscosity at which pointthe reaction mixture was removed from the heat and MEHQ (70 mg) wasadded. It was allowed to cool down to room temperature while beingexposed to air in order to activate the MEHQ radical inhibitor. Uponcooling the reaction product was homogeneous, clear, colorless oil (200g). The viscosity of the product was 100 cP at 25° C. RI (E-line) was1.5504 and Abbe was 30.9. The resulting product was stored at 4° C.

Example 9 Prepolymerization of the Material Described in Example 4 (60%)and Styrene (40%)

The procedure of Example 8 was followed except that the followingmaterials in the amounts indicated were used: material made according tothe procedure of Example 4 (180 g), styrene (120 g), Vazo 67 (0.225 g),and MEHQ (70 mg). Upon cooling the reaction product was homogeneous,clear, colorless oil (300 g, 100% yield). The viscosity of the productwas 1195 cP at 25° C. RI (E-line) was 1.5513 and Abbe was 30.8. Theresulting product was stored at 4° C.

Example 10 Prepolymerization of TGMA (70%), MMA (20%) and PTMA (10%)

A 100 mL round-bottom flask fitted with a condenser and a magnetic stirbar was charged with TGMA made according to the procedure of CE-1 (28g), MMA (8 g) and PTMA (4 g) under a nitrogen atmosphere. LUPEROX® 256peroxide (0.4 g) was added and the reaction mixture was heated to 70° C.in an oil bath. While heating, the viscosity of the reaction mixture at25° C. was monitored every 15 minutes. After 2 hour at the abovetemperature the reaction reached a stable viscosity at which point thereaction mixture was removed from the heat. It was allowed to cool downto room temperature while being exposed to air (in order to activate theMEHQ radical inhibitor introduced through the TGMA). Upon cooling thereaction product was homogeneous, clear, colorless oil (40 g) withviscosity 595 cP at 25° C. The resulting product was stored at 4° C. RI(E-line) was 1.5200 and Abbe was 43.3.

Example 11 Preparation of Prepolymer Containing TGMA (54%), Styrene(36%) and BPA-TDGE (10%)

A 100 mL round-bottom flask fitted with a condenser and a magnetic stirbar was charged with TGMA made according to the procedure of CE-1 (21.6g), styrene (14.4 g) and BPA-TDGE (4.0 g) under a nitrogen atmosphere.LUPEROX® 256 peroxide (0.04 g) was added and the reaction mixture washeated to 95° C. in an oil bath. While heating, the viscosity of thereaction mixture at 25° C. was monitored every 15 minutes. After 1 hourat the above temperature the reaction reached a stable viscosity atwhich point the reaction mixture was removed from the heat. It wasallowed to cool to room temperature while being exposed to air in orderto activate the MEHQ radical inhibitor introduced through the TGMA. Uponcooling, the reaction product was homogeneous, clear, colorless oil (40g) with viscosity 150 cP at 25° C. The product was stored at 4° C. RI(E-line) was 1.5520 and Abbe was 31.5. The BPA-TDGE used in thisexperiment was synthesized by reacting Bisphenol A diglycidyl ether withthiourea in the same process used to prepare CE-1.

Part 4—Procedure Used for Casting a Polymer Sample of Examples 1, 2,8-11 and CE-1

The casting formulations (CF) listed in Tables 1 and 2 were added to aglass jar and mixed until homogeneous. The radical initiator and basecatalyst were added to this mixture and stirred until fully dissolved.The resulting material was filtered through a 0.45 micron filter anddegassed under vacuum for 10 min and poured into a glass mold. The castmaterial was cured for 26 hours at gradually increasing temperature from70° C. to 95° C. (Cure Cycles 1 and 3) or for 25 hours at graduallyincreasing temperature from 50° C. to 120° C. (Cure Cycle 2). The samplewas demolded and postcured for 3 hours at 120° C. The curing cycles arelisted in Table 3 and the properties of the cast polymers are includedin Table 4 and 5.

TABLE 1 Casting Formulations CF-1 to CF-7 of Examples 1 and 2 CF-1 CF-2CF-3 CF-4 CF-5 CF-6 CF-7 Example # & Monomer Composition (% Weight)Example 1 88 Example 2 96 100 88 86 88 97 DVB 10 10 10 10 DMDS 4 2 4 GST2 2 3 Catalysts TBPB 1.00 0.72 0.72 1.00 0.80 1.00 1.00 LUPEROX ® 2561.00 1.00 1.30 1.00 1.00 1.00 1.00 Cure Cycle 1 X X X X 2 X 3 X X

TABLE 2 Casting Formulations CF-8 to CF-14 of Comparative Example 1(CE-1) and Examples 8-11 CF-8 CF-9 CF-10 CF-11 CF-12 CF-13 CF-14 Example# & Monomer Composition (% Weight) CE-1 96 75 Example 8 90 Example 9 9089 Example 10 100 Example 11 90 BPA-TDGE 10 DVB 4 10 10 10 10 DMDS GST25 2 3 Catalysts TBPB 0.72 1.00 1.00 1.00 0.72 0.72 DABCO 0.40 LUPEROX ®256 100 1.40 1.00 1.00 1.00 1.00 0.43 Curing Cycle 1 X 2 X X 3 X X X X

TABLE 3 Cure Cycles 1, 2 and 3 Cure Cycle 1 Cure Cycle 2 Cure Cycle 3Temper- Temper- Temper- Step Time ature Time ature Time ature # (hours)(° C.) (hours) (° C.) (hours) (° C.) 1 0.5 71-74 24 50-120 0.5 71-74 26.5 74 1 120 3.5 74 3 0.5 74-77 0.5 74-77 4 6.5 77 3.5 77 5 0.33 77-790.33 77-79 6 2.5 79 2.5 79 7 0.5 79-82 0.5 79-82 8 2.5 82 1.5 82 9 182-88 1 82-88 10 2 88 1 88 11 1.17 88-95 1.17 88-95 12 2 95 1 95

TABLE 4 Properties of Polymers made with Examples 1 (CF-1) and 2 (CF2-7)Properties CF-1 CF-2 CF-3 CF-4 CF-5 CF-6 CF-7 FMH 146 126 144 130 131145 135 RI 1.588 1.591 1.484 1.590 1.593 1.589 1.589 Abbe 35 36 37 35 3637 37 Thermal Good* Good* Good* Good* Good* Good* Good* PropertiesAppearance Clear Clear Clear Clear Clear Clear Clear YI 4.00 3.68 3.423.70 3.10 3.10 3.60 *Thermal properties are good when the Tg of thepolymerizate is >80° C. (DMA).

TABLE 5 Properties of Polymers made with CE-1 (CF-8 & 9) and Examples8-11 (CF-10-14) Properties CF-8 CF-9 CF-10 CF-11 CF-12 CF-13 CF-14 FMH125 72 136 151 145 103 148 RI 1.590 1.382 1.590 1.591 1.591 1.562 1.590Abbe 37 38 36 36 36 45 36 Thermal Bad** Bad** Good* Good* Good* Good*Good* Properties Appearance Clear Hazy Clear Clear Clear Clear Clear YI3.25 10.74 5.80 4.10 3.42 6.67 4.39 **Thermal properties are bad whenthe Tg of the polymerizate is <80° C. (DMA). Such materials are notacceptable for optical material and can not be processed as a lens.

The present invention has been described with reference to specificdetails of particular embodiments thereof. It is not intended that suchdetails be regarded as limitations upon the scope of the inventionexcept insofar as and to the extent that they are included in theaccompanying claims.

What is claimed is:
 1. A thioepoxide functional, polymerizablecomposition comprising a reaction product of: (a) thiourea; and (b) anepoxide functional, polymerizable composition comprising a reactionproduct prepared from a reaction mixture comprising: (i) a monomercomprising at least one ethylenically unsaturated ester functionalmonomer having an epoxide functional group; and (ii) a compound havingtwo or more thiol groups; wherein the reactants (i) and (ii) are reactedvia a Michael addition reaction in the presence of a base to form anepoxide functional reaction product.
 2. A polymerizable compositioncomprising a reaction product of: (a) a monomer composition comprisingat least one ethylenically unsaturated ester functional monomer having athioepoxide functional group; and (b) a thioepoxide functional,polymerizable composition comprising a reaction product of: (1)thiourea; and (2) an epoxide functional, polymerizable compositioncomprising a reaction product prepared from a reaction mixturecomprising: (i) a monomer comprising at least one ethylenicallyunsaturated ester functional monomer having an epoxide functional group;and (ii) a compound having two or more thiol groups; wherein thereactants (i) and (ii) are reacted via a Michael addition reaction inthe presence of a base to form an epoxide functional reaction product.3. The polymerizable composition of claim 2 wherein the monomercomposition (a) further comprises at least one different polymerizableethylenically unsaturated monomer.
 4. The polymerizable composition ofclaim 3 wherein the different polymerizable ethylenically unsaturatedmonomer comprises at least one of styrene, divinyl benzene, an alkylacrylate, and an alkyl methacrylate.
 5. An optical article comprising apolymer prepared from the polymerizable composition of claim
 4. 6. Amethod of preparing an optical article comprising: (1) reactingtogether: (a) a monomer comprising at least one ethylenicallyunsaturated ester functional monomer having an epoxide functional group;and (b) a compound having two or more thiol groups; wherein thereactants (a) and (b) are reacted via a Michael addition reaction in thepresence of a base to form an epoxide functional reaction product; (2)reacting the epoxide functional reaction product formed in step (1) withthiourea to form a thioepoxide functional, polymerizable composition;(3) mixing the thioepoxide functional, polymerizable composition formedin step (2) with: (a) a polymerizable composition comprising at leastone ethylenically unsaturated (meth)acrylate functional monomer having athioepoxide functional group; (b) an addition polymerization initiator;and (c) a catalyst to form a reaction mixture; (4) introducing thereaction mixture formed in step (3) to a mold of a desired shape at atemperature and for a time sufficient to form a polymerizate; and (5)releasing the polymerizate from the mold to yield an optical article. 7.The method of claim 6 wherein the polymerizable composition (a) used instep (3) comprises a prepolymer having a viscosity of 50 to 500centipoise measured at 25° C., prepared by polymerizing theethylenically unsaturated ester functional monomer having a thioepoxidefunctional group and optionally at least one different polymerizableethylenically unsaturated monomer in the presence of an azo initiator.8. The method of claim 7 wherein the prepolymer is prepared bypolymerizing styrene with the ethylenically unsaturated ester functionalmonomer having a thioepoxide functional group and optionally at leastone different polymerizable ethylenically unsaturated monomer.
 9. Themethod of claim 6 wherein immediately prior to introducing the reactionmixture to the mold, at least one different polymerizable ethylenicallyunsaturated monomer is added to the reaction mixture.
 10. The method ofclaim 6 wherein immediately prior to introducing the reaction mixture tothe mold, at least one compound having two or more beta-epithiopropylfunctional groups but no polymerizable ethylenically unsaturated groupsis added to the reaction mixture.
 11. The method of claim 10 wherein thecompound having two or more beta-epithiopropyl functional groups but nopolymerizable ethylenically unsaturated groups is a reaction product of2,2-bis(4-glycidyloxyphenyl)propane and thiourea.
 12. An optical articleprepared using the method of claim
 6. 13. A method of preparing anoptical article comprising: (1) reacting together reactants: (a) amonomer comprising at least one ethylenically unsaturated esterfunctional monomer having an epoxide functional group; and (b) acompound having two or more thiol groups; wherein the monomer (a) ispresent in stoichiometric excess and the reactants (a) and (b) arereacted via a Michael addition reaction in the presence of a base toform a product mixture comprising an epoxide functional reaction productand excess monomer (a); (2) reacting the product mixture formed in step(1) with thiourea to form a thioepoxide functional, polymerizablecomposition; (3) preparing a prepolymer reactant mixture by: (i) mixingthe thioepoxide functional, polymerizable composition formed in step (2)with: (a) a first polymerizable composition comprising at least oneethylenically unsaturated monomer; and (b) an azo additionpolymerization initiator to form a reaction mixture; and (ii) allowingethylenically unsaturated groups in the reaction mixture formed in (i)to polymerize to form a prepolymer having a threshold viscosity of 50 to500 centipoise measured at 25° C., wherein the azo additionpolymerization initiator is present in an amount sufficient only toachieve the threshold viscosity; (4) mixing the prepolymer reactantmixture formed in step (3) with: (a) an initiator package that isessentially free of azo initiators; and (b) a second polymerizablecomposition comprising at least one ethylenically unsaturated monomerhaving two or more ethylenically unsaturated groups to form a moldablecomposition; (5) introducing the moldable composition formed in step (4)to a mold of a desired shape at a temperature and for a time sufficientto form a polymerizate; (6) releasing the polymerizate from the mold toyield an optical article.
 14. The method of claim 13 wherein in step(1), the equivalent ratio of ethylenically unsaturated groups in themonomer (a) to thiol groups in the compound (b) is greater than 1.1:1.15. The method of claim 13 wherein in step (4), the initiator package(a) comprises peroxy functional initiators and a catalyst.
 16. Themethod of claim 13 wherein in step (4), the second polymerizablecomposition (b) comprises divinylbenzene.
 17. An optical articleprepared using the method of claim 13.